In nozzle per spot ink jet printers, the print quality is dependent upon the effective center-to-center distance of adjacent nozzles in an array. In known nozzle technologies relatively close center-to-center distance are achievable, for example, on the order of 3 or 4 mils. This, however, results in a fragile array due to the close centering of the respective nozzles.
The use of laterally staggered multiple arrays as set forth in U.S. Pat. RE. No. 28,219 to Taylor et al. provides an alternative to fabricating nozzles on close centers, while introducing at least two problems.
The first problem is that additional timing networks are utilized to permit the staggered array of Taylor et al to effectively emulate one line of nozzles. That is, for a staggered array of two rows of nozzles, for example, the print signal applied to the upper row of nozzles must be delayed or advanced with respect to the print signal applied to the lower row of nozzles dependent upon the direction of travel of the printing medium, such that the droplets from the two rows of nozzles are sequentially applied a row at a time to form a single line on the printing medium.
The second problem deals with the gutter structure and required deflection voltages. If a single gutter is used, then non-printing droplets from both rows of nozzles must be deflected to the single gutter. This requires a higher deflection voltage than is used for a single row of nozzles due to the different and substantially parallel droplet trajectories from the two rows. Two gutters may be used as in Taylor et al, but this results in a more complex physical structure for the printer.
According to the present invention an ink jet printer including a staggered nozzle array is disclosed, in which the above-named problems are eliminated or at least substantially reduced. This is accomplished by having the droplet streams from at least one of the rows emanate off-normal with respect to the plane of the nozzle plate, resulting in the droplets from the respective rows concurrently converging in non-parallel trajectories to form a single line at a given time on the printing medium. Accordingly, the need for complex timing circuitry to achieve line at a time printing from a staggered nozzle array is substantially reduced. This is so, since all of the dot positions of a line which is to be printed, are printed concurrently by the jets emanating from the respective rows of nozzles, rather than sequentially, that is by a row of nozzles at a time, as disclosed by Taylor et al.
Further, since the gutter is relatively close to the printing medium, the upper set of droplet streams require only slightly more deflection than the lower set of droplet streams in order to gutter the respective droplets. This is so, since the respective droplet streams are converging towards the respective dot positions of the line as they approach the printing medium. Therefore, a deflection voltage may be used for the respective droplet streams which is essentially the same as would be used for a single row of streams, since each droplet stream is substantially the same distance from the gutter as they near the printing medium, resulting in the droplets from the respective streams striking the gutter relatively close to one another.